The price reporting agency at the centre of the European investigation into allegations of oil price fixing recently argued with a key international watchdog that there was no need for its benchmarks to be brought under the oversight of an outside regulator.

Platts, which is based in New York and owned by US publisher McGraw-Hill, said transparency and independence were the key to robust energy benchmarks and said they should be free from "undue influence, including from public institutions".

The agency was responding to a consultation document put out last year by the International Organisation of Securities Commissions (Iosco) and its response was published by the body two months ago.

"Platts believes that benchmark submissions should not be a regulated activity and that any perceived benefits would be far outweighed by the significant disadvantages of doing so," it said, using exactly the same wording to argue in the same letter against a similar move to regulate benchmark administration.

"By raising the regulatory burden on data reporting activity, such action would likely cause a retreat from participation in price discovery processes in general. This would in turn affect the amount and quality of information supporting benchmarks, which would be incompatible with regulatory goals and ultimately detrimental to the effective functioning of the physical commodity markets," Platts said.

The agency also insisted it was not in the best interest of the wider oil market to establish an external oversight committee or other body to provide independent scrutiny, fearing it would create "market distortions".

Platts' offices were occupied for three days by the European commission this week and the agency is cooperating with inquiries it is believed were at least partly triggered by a complaint from a Hungarian biofuel producer, Pannonia Ethanol. The biofuel firm said it approached Platts last spring to contribute to the "market-on-close" window but was refused, according to Reuters.

Platts said it was following established procedure to vet new participants and last night pointed to a Bloomberg report which claimed that 34 out of 55 traders, brokers and analysts surveyed said the pricing system run by Platts was the best way to determine prices in the $3.4tn-a-year market for crude and refined oil products.

Statoil, the Norwegian oil and gas group which was raided along with BP and Shell, admitted the suspected violations being looked at by Brussels may have been going on since 2002.

In a statement, the EC said: "The Commission has concerns that the companies may have colluded in reporting distorted prices to a Price Reporting Agency to manipulate the published prices for a number of oil and biofuel products."

The EC said none of the companies raided should be considered guilty at this stage but analysts said it was not good for reputations, not least BP, which sacked some of its traders and paid a $300m fine in the US after the Commodity Futures Trading Commission accused it in 2006 of trying to manipulate the propane gas market.

A Platts spokesman said: "Platts is supportive of efforts by legislators and regulators to improve the functioning of the oil markets and other physical commodities markets that it covers… Platts' core mission is to publish price assessments which are reflective of true market value. Platts has cautioned against any oversight which would dissuade market submitters from participating in the price formation process. That said, Platts fully recognizes that market participants and the public want to have confidence that Platts takes its role and responsibilities seriously and is willing to demonstrate that it does."